Observations of High-redshift Early-Type Galaxies
= Fact and References = Observations of High-Redshift Early-Type and/or Quiescent Galaxies * Ample evidence now exists for the presence of massive galaxies at z>2 with little or no ongoing star formation, suggesting that a non-negligible fraction of the local early-type galaxy population was effectively in place only a few Gyr after the big bang, and that massive red galaxies constitute a signiﬁcant fraction of (or possibly even dominate) the stellar mass density at z~2 (e.g., McCarthy et al. 2004; Labbe et al. 2005; Daddi et al. 2005; Kriek et al. 2006, 2008a; Rudnick et al. 2006; Marchesini et al. 2007; Stutz et al. 2008; Toft et al. 2009) * The quiescent galaxies form a signiﬁcant fraction (30 − 50%) of all massive z~2 galaxies (e.g. Kriek et al. 2006; Williams et al. 2009; Toft et al. 2009) arXiv:1212.1158 * At 0<1, the ETG stellar mass function shows a downsizing evolution, with the majority of massive ETGs ($M>10^{11}M_{\odot}$) already in place at z~0.7 (Pozzetti et al. 2010) * The number density of ETGs grew rapidly from z>3 to z~1 (e.g Fontana et al. 2009; Brammer et al. 2011; Dominguez-Sanchez et al. 2011). Size Evolution * Galaxies with stellar masses of ~$10^11M_{\odot}$ at z= 1.5−2.5 are '''much more compact' than galaxies of similar mass at z = 0, particularly those with the lowest star formation rates (Daddi et al. 2005; Papovich et al. 2005; Trujillo et al. 2006, 2007; Toft et al. 2007; Longhetti et al. 2007; Zirm et al. 2007; van Dokkum et al. 2008; Cimatti et al. 2008; Buitrago et al. 2008; van der Wel et al. 2008; Franx et al. 2008; Buitrago et al. 2008; Stockton et al. 2008; Damjanov et al. 2009; Williams et al. 2009; Saracco, Longhetti & Adnreon 2009; Cassata et al. 2010, 2011; Saracco et al. 2010; Mancini et al. 2010; Damjanov et al. 2011; Newman et al. 2011) ** Considering the low intrinsic scatter in the Fundamental Plane (Djorgovski & Davis 1987; Hyde & Bernardi 2009; Gargiulo et al. 2009) Possible Error Sources to Size Measurement # Photometric redshift # Mass estimation (see Muzzin et al. 2009a,b) #* Uncertainties in stellar population synthesis codes, the IMF, the treatment of dust, star formation histories, and metallicities can easily introduce systematic errors of 0.2–0.3 dex (see, e.g., ''Drory, Bender, & Hopp 2004; van der Wel et al. 2006; Wuyts et al. 2009; Muzzin et al. 2009a; Marchesini et al. 2009) #* These uncertainties (library, IMF, et al. ) can result in systematic errors of up to a factor of 6 (Conroy et al. 2009) #* At low redshift, there is good agreement between stellar masses determined by photometric SED ﬁtting methods and dynamical masses (Taylor et al. 2010a). #* Whether this is also the case at high redshift is unclear (e.g., van de Sande et al. 2011; Bezanson et al. 2011; Martinez-Manso et al. 2011) # From half-Light radius to half-Mass radius or Color gradient # Depth of the imaging data (Hopkins et al. 2009a, Mancini et al. 2009) #* This could be a problem considering that this is the place where most of the growth happened (Bezanson et al. 2009; Naab et al. 2009) #* However, see presentation for the Jan.2010 AAS Meeting from Chien. Peng #* Previous studies have shown that reliable galaxy sizes can be measured from ground-based data, provided the signal-to noise ratio is sufﬁciently high and the PSF across the image is stable (e.g., Trujillo et al. 2006b; Franx et al. 2008). #* Szomoru et al. (2010) carried out an analysis on a z = 1.91 compact quiescent galaxy in the Hubble Ultra Deep Field (HUDF) and conﬁrmed its small size. # Rest-frame UV v.s. rest-frame optical (see Trujillo et al. 2007, Mancini et al. 2009) # Central point-source contamination or AGN * Their surface densities likewise evolve strongly with redshift, as does the “threshold” surface density above which galaxies are predominantly quiescent (Franx et al. 2008; Maier et al. 2009). Stellar Kinematics * Measurements of velocity dispersion and dynamical masses for z>1.5 massive galaxies (Cenarro & Trujillo 2009; van Dokkum, Kriek, & Franx 2009a; Cappellari et al. 2009; Onodera et al. 2010; van de Sande et al. 2011) Environment and related topics * Evidence for accelerated structural evolution in denser regions: *# Stott et al. (2011) report that the sizes of the most massive galaxies in clusters increase by at most 30% during the period of z=1–0.2. *# Cooper et al. (2012) ﬁnd a correlation between the sizes and local galaxy overdensity for early-type galaxies at 0.4 < z < 1.2, suggesting accelerated morphological evolution in higher density regions. *# Zirm et al. (2012) ﬁnd a hint of evidence that massive quiescent galaxies in the vicinity of radio galaxy MRC 1138−262 at z = 2.2 have larger sizes at ﬁxed mass compared to galaxies in the ﬁeld at this redshift. *# Papovich et al. (2012): For a proto-cluster at z~1.6, the cluster quiescent galaxies have larger average effective sizes compared to ﬁeld galaxies at ﬁxed mass at greater than 90% signiﬁcance. * Galaxy assembly via mergers is most effective in small groups and forming clusters at lower redshifts, because these systems have lower velocity dispersions (see Tran et al. 2008; McIntosh et al. 2008; McGee et al. 2009; Wilman et al. 2009) * Evidence against accelerated structural evolution in denser region ** See Rettura et al. 2010 * Measurements of the galaxy merger rate in high-density regions (such as clusters) show that these mergers occur mainly without star formation (Ellison et al. 2010). (Mergers involving even small amounts of star formation are disfavored by the measured evolution of the colors of cluster galaxies down to lower redshift; van Dokkum & van der Marel 2007.) * For z~1.6 cluster in Papovich et al. 2012, the most massive galaxies in the cluster are still only 10%–50% as massive as the brightest galaxies in low-redshift clusters (Blakeslee et al. 2006; Holden et al. 2009; Valentinuzzi et al. 2010). These galaxies need to increase both their stellar masses and their effective sizes by at least a factor of two. Simulations predict that the growth of massive cluster galaxies at “late” times (z<1.5) should occur more through the dissipationless mergers of relatively massive progenitors (e.g., De Lucia & Blaizot 2007; Ruszkowski & Springel 2009). Theoretical Explanations, Simulation and Modelling Interpretation of the Evolution of Size and other properties # Dramatic mass loss from AGN feedback (Fan et al. 2008) # A fading merger-induced star burst (Hopkins et al. 2009c) # A combination of selection effects and mergers (van der Wel et al. 2009) # (Minor) Mergers (Naab et al. 2007; Naab, Johansson, & Ostriker 2009; Bezanson et al. 2009; Khochfar & Silk 2008; Hopkins et al. 2009b; Feldmann et al. 2009) #* Some observational estimates of the '''major dry merger rate since z~1 indicate that these are indeed a factor in the buildup of massive galaxies (Bell et al. 2006; Bundy et al. 2009; de Ravel et al. 2009) #* Minor mergers may be a more important process—both from a simple virial argument (Naab et al. 2009) and because massive compact “cores” at high redshift may accrete material in their outskirts to form the massive ellipticals seen today (Bezanson et al. 2009; Hopkins et al. 2009a; van Dokkum et al. 2010). #* Other references for (minor) disspationless merger model (Loeb & Peebles 2003; van Dokkum 2005; Bell et al. 2006; Lotz et al. 2008; Masjedi et al. 2008; van der Wel et al. 2009a, 2011) [NEED CHECK!!!] #* Minor mergers would cause the galaxies to add mass at larger radii, increasing their effective sizes substantially with a relatively small increase in stellar mass (Oser et al. 2010). #* Although this explanation would not explain the substantially larger central densities of high-redshift ellipticals compared to galaxies at lower redshift (see, e.g., Stockton et al. 2010) * Alternatively, Graham (2011) notes that many of these compact objects share sizes, masses, and mass densities of present-day bulges, suggesting that some of these objects are the precursors to the spheroidal components of present-day disk galaxies. * Theoretical models have yet to converge on a deﬁnitive explanation—some proposed models predict galaxy sizes dramatically different from those observed (Joung et al. 2009; simulated galaxies are too small), while others match observed sizes at z=2 and z=0 (Khochfar & Silk 2006) but not at z~1 (van der Wel et al. 2008). Evidence from Local Early-Type Galaxies Nearby Analogs of Compact Quiescent Galaxies * Observations and on the rarity of local compact quiescent galaxies: (Trujillo et al. 2009; Taylor et al. 2009b) * The existence of compact low-z ETGs with sizes and masses comparable to those of compact ETGs at z > 2 is somehow unclear, with some results showing an absence of such galaxies (e.g. Taylor et al. 2010) and others ﬁnding a few candidates (e.g. Valentinuzzi et al. 2010; Shih & Stockton 2011) = Papers and References = * The Growth of Massive Galaxies Since z = 2 ** van Dokkum, Whitaker, Brammer, Franx, Kriek, Labbe et al. 2010 ApJ *** \bibitemDokkum et al.(2010){2010ApJ...709.1018V} van Dokkum, P.~G., Whitaker, K.~E., Brammer, G., et al.\ 2010, \apj, 709, 1018 ** galaxies selected by constant number density rather than mass from NMBS and OBEY; surface brightness profiles are measured from stacking images ** massive galaxies gradually built up their outer regions over the past 10 Gyr. ** massive galaxies have grown mostly inside-out, assembling their extended stellar halos around compact, dense cores with possibly exponential radial density distributions. ---- * The Evolving Relations Between Size, Mass, Surface Density, and Star Formation in 3×10^4 Galaxies Since z = 2 ** Williams, Quadri, Franx, van Dokkum, Toft, Kriek & Labbe 2010 ApJ ** \bibitemet al.(2010){2010ApJ...713..738W} Williams, R.~J., Quadri, R.~F., Franx, M., et al.\ 2010, \apj, 713, 738 ** Both the sizes and surface densities of quiescent galaxies evolve strongly from z=2–0 ** Higher-mass quiescent galaxies undergo faster structural evolution, consistent with previous results. ** Interestingly, star-forming galaxies’ sizes and densities evolve at rates similar to those of quiescent galaxies. It is therefore possible that the same physical processes drive the structural evolution of both populations, suggesting that “dry mergers” may not be the sole culprit in this size evolution. ** Selected from UKIDSS Ultra-Deep Survey ---- * CANDELS Observations of the Structural Properties of Cluster Galaxies at z = 1.62 ** Papovich, Bassett, Lotz, van der Wel, Tran, Finkelstein, Bell, Conselice et al. 2012 ApJ ** \bibitemet al.(2012){2012ApJ...750...93P} Papovich, C., Bassett, R., Lotz, J.~M., et al.\ 2012, \apj, 750, 93 ** The size distribution of the quiescent cluster galaxies shows a deficit of compact (<1 kpc), massive galaxies compared to CANDELS field galaxies at z = 1.6. ** physical processes associated with the denser cluster region seem to have caused accelerated size growth in quiescent galaxies prior to z=1.6 ** The quiescent cluster galaxies at z = 1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. ---- * Sizes and Surface Brightness Profiles of Quiescent Galaxies at z ~ 2 ** Szomoru, Franx & van Dokkum 2012 ApJ ** \bibitemet al.(2012){2012ApJ...749..121S} Szomoru, D., Franx, M., \& van Dokkum, P.~G.\ 2012, \apj, 749, 121 ** Most of the mass growth which occurs between z~2 and z=0 must be due to accretion of material onto the outer regions ** Quiescent galaxies at z~2 very closely follow Sersic proﬁles, ´with n_{median}=3.7, and have no excess ﬂux at large radii. ---- = People = * Pieter van Dokkum Yale University * Daniel Szomoru Leiden University * Casey Papovich TAMU * Ignacio Trujillo Instituto de Astrofísica de Canarias * Arjen van der Wel Max-Planck Institure for Astronomy in Heidelberg * Andrea Cimatti Bologna University * Rachel Bezanson Yale University * Ludwig Oser Max-Planck-Institut für Astrophysik = Specific Questions = Mass Evolution or Growth of Massive Galaxies * van Dokkum et al. 2010 ** Number density selected objects. * Bell et al. 2004b ** Using B-band Luminosity function of early-type galaxies in COMBO-17 to study the luminosity evolution from z=1.1 to z=0.2. ** Accounting for the change in stellar mass-to-light ratio implied by the redshift evolution in red galaxy colors, the COMBO-17 data indicate an increase in stellar mass on the red sequence by a factor of two since z~1. * Johansson, Naab & Ostriker 2012 ** Simulation for the formation of massive early-type galaxies.